There are many types of light fixtures available to architects and engineers for utilization in new construction or renovation. In most instances the type of fixture used depends on the ceiling construction. When inverted tee-bar suspended ceilings are used the grid defined thereby is a standard size and a simple box-type fixture may be positioned in the ceiling so that its edges rest on the flanges of the grid defining the ceiling opening. When wall-board type ceilings are used, more expensive fixtures having exposed flanges and "swing-out" hangers (or other awkward mounting hardware) must be used. In the latter case the fixture has means for mounting the housing thereof to the ceiling and further means for permitting access to the interior for repair or replacement of the component parts.
In the suspended grid type of ceiling repair is effected by simply removing the entire fixture from the grid by bringing it down through the ceiling opening. The fixture is not permanently attached to the ceiling as in the latter case.